I've noticed several breeders of questionable reputation force people adopting pups to sign a contract saying they will feed their pup "NuVet" supplement on a daily basis, otherwise their health guarantee is "null and void" (not mentioning names here - but one of them also says their Vs are from "Hungry").
Here is some specific wording from a contract I found:
guarantee will be null and void if Buyer does not supply the dog with
NuVet Plus for Canines® on a daily basis. Buyer is required to use NuVet
Labs ™ NuVet Plus for Canines® on a daily basis, during and after the
guarantee period, failure to do so will make this guarantee null and
void. NuVet Plus for Canines® may be ordered @ (800) 474-7044
order code # ------, make sure that you use the order code number when
ordering, it allows us to track your purchase of vitamins."
(Code removed to prevent purchases under the breeder.)
I'm guessing that these breeders get some kind of a kick-back from NuVet for requiring the supplements...
I've never heard of a reputable breeder requiring buyers to give their
puppies a supplement (and using a signed contract to try and force it).
A reputable breeder would NEVER force you to sign a contract saying you will give your puppy a specific supplement or food. They will recommend food brands - pay attention to what they feed their dogs. Good breeders won't feed cheap kibble full of fillers (corn, grains, and soy).